This invention relates generally to a torque control crescent oil pump, having low parasitic loss and rapid pressure transient response, and to a method for controlling oil flow within the pump.
Crescent oil pumps are widely used in automatic transmissions, engines, and other similar applications to control torque. A crescent oil pump typically comprises a sealed housing having an inlet port and a discharge port, a driving inner gear rotating within the housing along one axis, and a driven outer gear rotating within the housing along a second offset axis. External gear teeth on the driving gear mesh with internal gear teeth on the driven gear between the inlet and the discharge ports. In such manner, the discharge port is sealed from the inlet port in the direction of rotation of the driving and the driven gears. External and internal troughs on the driving and driven gears between the gear teeth define pump chambers, which transfer fluid from the inlet port to the outlet port as the gears rotate.
The teeth of the inner and outer gears separate from each other at the bottom band of the gears due to the offset axes. The bottom band of the gears is typically sealed using a stationary crescent shaped body machined into the housing between the external teeth of the inner gear and the internal teeth of the outer gear. The crescent shaped body has a pair of arc-shaped walls which closely fit around the inner and outer gears. The arc-shaped walls cooperate with the tips of the external teeth of the inner gear, and cooperate with the tips of the internal teeth of the outer gear to define fluid seals against leakage from the discharge port to the inlet port.
Crescent pump gear systems are often used in pumps with high-pressure applications. The sealing capability of the gears against the crescent is enhanced due to the number of teeth on both the inner and outer gears that seal across the crescent.
However, crescent oil pumps typically have high parasitic loss resulting from oil circulation at low pressure through restrictive hydraulic circuits. Parasitic loss results in poor fuel economy, and produces undesirable wheel torques. Two types of variable displacement pumps, piston and vane, are not restrictive, but are slow and have high control forces.
It is necessary to develop a torque control crescent oil pump, having low parasitic loss and rapid pressure transient response, to be more fuel efficient while being capable of rapidly delivering peak torque.
It is in general an object of the invention to provide a torque control crescent oil pump, having low parasitic loss and rapid pressure transient response, and to provide a method for controlling oil flow within the pump.
In one aspect, this invention provides a crescent oil pump comprising a housing, an externally toothed annular gear capable of rotation about a first axis, and an internally toothed annular gear capable of rotation about a second axis. It further comprises a crescent body adapted to move from a first position to a second position. When in the first position, the crescent body is adapted to form at least one seal between a portion of the externally toothed annular gear and a portion of the internally toothed annular gear. When in the second position, the crescent body is positioned so that it does not form a seal between the portion of the externally toothed annular gear and the portion of the internally toothed annular gear.
In another aspect, this invention provides a crescent oil pump comprising a housing, an externally toothed annular gear capable of rotation about a first axis, and an internally toothed annular gear capable of rotation about a second axis. It further comprises an actuating device and a crescent body adapted to move from a first position to a second position by the actuating device.
In yet another aspect, this invention provides a method of controlling oil flow within a crescent oil pump. First, a crescent oil pump is provided comprising a housing, an externally toothed annular gear capable of rotation about a first axis, and an internally toothed annular gear capable of rotation about a second axis. The crescent oil pump further comprises an actuating device, and a crescent body adapted to move from a first position to a second position by the actuating device. The crescent body is then moved to the first position using the actuating device to restrict oil flow within the housing. Finally, the crescent body is moved to the second position using the actuating device to permit oil flow within the housing.
The present invention, together with further object and advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.